This invention relates generally to injection molding and more particularly to a nozzle for hot runner molding which has high strength and does not require a heating element.
A variety of different nozzles seated in the mold with a central melt bore extending therethrough are used to convey melt towards the gate. These nozzles are usually heated, with steel nozzles having heaters mounted around them being used at one time. A well known heated nozzle is shown in the applicant's U.S. Pat. No. 4,355,460 which issued Oct. 26, 1982. In that case, an electrical heating element is wound in a space between an inner core portion and an outer casing and the space is then filled with highly conductive beryllium copper to surround the heating element and form an integral heated nozzle. While these work very well for most applications, they are relatively costly to make and the heating element is subject to malfunction. Furthermore, in some applications they do not have sufficient strength to withstand the repeated impact of the very high injection pressures required.
More recently, as seen in the applicant's U.S. Pat. No. 5,206,040 which issued Apr. 27, 1993, a nozzle or sealing element is shown without an electrical heating element. However, in this case the nozzle has the disadvantage that an elongated shaft or torpedo extending in its central bore is required to provide sufficient thermal conductivity.